Method and apparatus for restricting fluid flow in a downhole tool

ABSTRACT

A ball seat valve employed in a downhole tool string includes a split-ring baffle that is configured to radially expand and to radially contract to catch a dropped ball.

BACKGROUND

This disclosure relates generally to ball-operated valves, and morespecifically to such valves having a ball-receiving baffle, and toconfigurations for such baffles.

Subterranean well operations commonly employ valves at differentlocations along a wellbore for a variety of purposes. In someapplications, downhole valves are employed to isolate sections ofconduit within a wellbore. Such valves can be individually actuatedopened/closed to isolate different portions of a string of conduitsalong the length of the wellbore. One type of valve employed insubterranean wells is a ball seat valve.

A typical ball seat valve has a bore or passageway that is restricted bya baffle forming a seat to receive a ball (which may literally be aspherical “ball” or in some examples may be another configuration of aplug or other mechanism that will engage the seat. The term “ball” asused herein, unless expressly indicated otherwise, refers to any sphereor other configuration of a plug intended to engage a baffle to close orsubstantially restrict a flow path through a tool. A ball can be droppeddown the conduit within a wellbore to be disposed on the seat. Once theball is seated, the fluid passage through the valve is closed andthereby prevents fluid from flowing through the bore of the ball seatvalve, which, in turn, isolates the conduit section in which the valveis disposed. As the fluid pressure above the ball builds up, the conduitcan be pressurized for any of a number of potential purposes, includingfor example, tubing testing, actuating a tool connected to the ball seatsuch as setting a packer, or fracturing particular layers of a formationthrough which the wellbore passes.

SUMMARY

Examples according to this disclosure include a split-ring baffle thatcan be employed in a ball seat valve in a conduit string of a wellbore.One example includes an apparatus for restricting fluid flow through adownhole tubular member. The apparatus, e.g., a ball seat valve,includes an annular sleeve and a resilient split-ring baffle. Theannular sleeve is configured to be received within an annular housingand has an inner surface defining a first section of a first diameterand a second section of a second, smaller, diameter. The split-ringbaffle is at least partially received within the sleeve. The baffleincludes a longitudinal seam forming two separate circumferential endsin the baffle. The baffle is also longitudinally moveable between afirst position in the first section and a second position in the secondsection of the sleeve. An outer surface of the baffle is configured toengage the inner surface of the sleeve to cause the baffle, when in thefirst position to be relatively radially expanded, and, when moved tothe second position in the sleeve, to radially contract.

The details of one or more examples of the disclosure are set forth inthe accompanying drawings and the description below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically depicts an example fracturing system including atool string arranged within a wellbore that passes through a number oflayers of a formation of a well.

FIG. 2 depicts a section view of a portion of a tool string including anexample ball seat valve in accordance with this disclosure.

FIGS. 3A-3C depict section views of an example split-ring baffle andannular sleeve arranged within the tool string of FIG. 2.

FIGS. 4A and 4B depict perspective views of an example split-ringbaffle.

FIG. 5 depicts a section view of a portion of a tool string, whichillustrates an example ball seat valve in a closed state with asplit-ring baffle expanded within a sleeve.

FIG. 6 depicts a section view of a portion of a tool string, whichillustrates an example ball seat valve in an open state with asplit-ring baffle contracted within a sleeve with a dropped ball seatedin the baffle.

FIG. 7 is a flowchart illustrating an example method of actuating anapparatus for restricting fluid flow through a downhole tubular member.

DETAILED DESCRIPTION

As noted above, ball seats can be employed to isolate different layersof a formation for fracturing. A fracturing system commonly includespumps that pressurize fracturing fluid, which may be communicateddownhole via the central passageway of a string of conduits disposedwithin a wellbore. The string can include sections with ball seat valvesthat are aligned with different layers of the formation. Opening andclosing the ball seat valves at different locations along the string isused to control fluid flow between the central passageway of the stringand different layers of the formation. For example, a ball seat can beactuated to isolate a particular section of conduit aligned with atarget layer of the formation. In combination with actuating the ballseat, one or more apertures in the conduit above the ball seat can beopened or exposed to allow fracturing fluid to pass through the conduitinto the target layer of the formation.

In practice, a ball seat valve can be activated by dropping a ball intothe string from the surface of the well. The dropped ball descendsthrough the conduit within the wellbore until it lodges in the seat ofthe valve. After the ball lodges in the ball seat, fluid flow throughthe central passageway of the string becomes restricted, a conditionthat allows fluid pressure to be applied from the surface of the wellfor purposes of exerting a downward force on the ball. The ball seattypically is attached to a sleeve of the valve to transfer the force tothe sleeve to cause the valve to open. However, in other examples, theseating of the ball in the ball seat and the fluidic isolation of theassociated zone of the tool string is separate from opening of the valveto allow fluid to pass through the tool string housing into thesurrounding formation. For example, a separate sleeve within the toolstring conduit can be actuated, e.g., moved axially to expose aperturesin the tool string conduit. Once the valve has been opened, fracturingfluid can be transmitted through the string of conduit to one or moreapertures opened/exposed by the value to carry out fracturing operationson a portion of the formation aligned with the ball seat valve. Thus,seating the ball in the ball seat fluidically isolates a particular zoneof the wellbore and the valve is then opened to allow fracturing fluidto pass through the tool string conduit into a particular region of theformation.

A fracturing system can employ multiple ball seat valves to formmultiple zones along the length of the wellbore. The zones of thewellbore can be used to target different layers of a formation forfracturing operations. In some fracturing systems, the valves maycontain many different size ball seats to enable remote operation of theball seat valves from the surface of the well. For example, to targetand actuate the valves, differently sized balls may be dropped into thestring from the surface of the well. Each ball size may be uniquelyassociated with a different valve, so that a particular ball size isused to actuate a specific valve. The smallest ball commonly opens thedeepest valve. The ball seats of the string have different diameters,which are respectively associated with the different sized balls.

In systems employing multiple ball seat valves of varying size, theannular area that is consumed by each ball seat along the stringrestricts the cross-sectional flow area through the string (even in theabsence of a ball), and the addition of each valve (and ball seat) tothe string further restricts the cross-sectional flow area through thecentral passageway of the string, as the flow through each ball seatbecomes progressively more narrow as the number of ball seats increase.Thus, a large number of valves may significantly restrict thecross-sectional flow area through the string.

To address the issue of progressively more restriction to the conduit ofthe string, multiple ball seat valves of the same size can be employed,in which the seat of each valve is configured to expand and contractsuch that the seat can selectively catch a dropped ball or allow theball to pass down the string to the next valve. In other words,adjustable ball seat valves can be employed that are capable of beingexpanded to larger diameters and contracted to smaller diameters. Theseat of a ball seat valve is, more generally, a baffle, configured toreceive a ball (or other plug, as noted earlier herein) to substantiallyblock movement of fluids through the conduit of the wellbore.

Examples according to this disclosure include a split-ring baffle thatcan be employed in a ball seat valve in a conduit string within awellbore. One example includes an apparatus for restricting fluid flowthrough a downhole annular member. The apparatus, e.g., a ball seatvalve, includes an annular sleeve and a resilient split-ring baffle. Theannular sleeve is configured to be received within an annular housingand has an inner surface defining a first section of a first diameterand a second section of a second, smaller, diameter. The split-ringbaffle is at least partially received within the sleeve. The baffleincludes a longitudinal seam forming two separate circumferential endsin the baffle. The baffle is also longitudinally moveable between afirst position in the first section and a second position in the secondsection of the sleeve. An outer surface of the baffle is configured toengage the inner surface of the sleeve to cause the baffle, when in thefirst position to be relatively radially expanded, and, when moved tothe second position in the sleeve, to radially contract.

Example split-ring baffles in accordance with this disclosure mayprovide a number of advantages. For example, split-ring baffles inaccordance with this disclosure provide a simple and low cost (e.g. bothmaterial and manufacturing) component that can include a relativelyshort length to reduce the overall size of a tool including the baffle.Additionally, the baffle only includes one junction to seal and whichreduces interaction between the baffle and materials transmitted throughthe tool string conduit. The baffle can include support structures forreducing the likelihood of deflection and to lock the baffle into atleast one position relative to the sleeve of the valve. The baffle canbe re-expanded to the full internal diameter of the sleeve and iscapable of being contracted and re-expanded multiple times withoutsignificant impacts on function.

Split-ring baffles in accordance with this disclosure are described asemployed as part of a ball seat valve used to isolate and target layersof a formation during fracturing operations. However, split-ring bafflesand ball seat valves in accordance with this disclosure can be employedin other applications. For example, a ball seat valve including asplit-ring baffle in accordance with this disclosure can be employed tocatch a dart employed for positive displacement in cementingapplications, to set mechanical packers, as part of a shut-off collar atthe toe of the tool in cementing applications, and in conjunction withliner hangers.

FIG. 1 is a schematic illustration of fracturing system 10 includingtool string 12 arranged within wellbore 14, which passes through anumber of layers of formation 18 of the well. Tool string 12 includes anumber of ball seat valves 20 in accordance with this disclosure. Toolstring 12 also includes a number of packers 22. Packers 22 seal off anannulus formed radially between tool string 12 and wellbore 14. Packersin this example are designed for sealing engagement with an uncased oropen hole wellbore 14, but if the wellbore is cased or lined, then casedhole-type packers may be used instead. Swellable, inflatable,expandable, and other types of packers can be used, as appropriate forthe well conditions, or no packers may be used.

In the FIG. 1 example, ball seat valves 20 permit selective fluidcommunication between the central passageway of tool string 12 and eachsection of the annulus isolated between two of the packers 22, which arelocated above and below each of the valves in wellbore 14. Each suchsection of the annulus surrounding tool string 12 is in fluidcommunication with a corresponding earth formation zone or layer offormation 18. Of course, if packers 22 are not used, then ball seatvalves 20 can be placed in communication with the individual zones byother mechanisms, for example, with perforations, etc.

The zones of formation 18 can be, for example, sections of the sameformation, or they may be sections of different formations. Each zonemay be associated with one or more of ball seat valves 20. In order tocarry out a fracturing operation on a particular one of the zones offormation 18, the associated ball seat valve 20 can be opened to allowcommunication between the central passageway of tool string 12 and theassociated zone.

For example, one of ball seat valves 20 can be activated by dropping aball into tool string 12 from the surface of the well. The dropped balldescends through the conduit forming string 12 within wellbore 14 untilit lodges in a seat of valve 20. In one example, ball seat valve 20includes an annular sleeve and a resilient split-ring baffle thatfunctions as the ball seat of valve 20. The split-ring baffle of ballseat valve 20 is at least partially received within the sleeve. An outersurface of the baffle is configured to engage the inner surface of thesleeve to cause the baffle, when in a first position to be relativelyradially expanded, and, when moved to a second position in the sleeve,to radially contract.

After the ball lodges in the ball seat, fluid flow through the centralpassageway of tool string 12 becomes restricted, a condition that allowsfluid pressure to be applied from the surface of the well for purposesof exerting a downward force on the ball. Additionally, after the balllodges in the ball seat, ball seat valve 20 can be opened to allowcommunication between the central passageway of tool string 12 and theassociated zone of formation 18. In one example, a sleeve is locatedwithin tool string 12 above the split-ring baffle in which the ball isseated. The sleeve can be configured to be actuated to move axiallywithin the outer conduit of tool string 12 to expose one or moreapertures in the conduit. In another example, the ball seat is attachedto a sleeve of ball seat valve 20 to transfer the force generated byfluid pressure in the central passageway of tools string 12 to thesleeve to cause the sleeve to move within the housing, thereby openingthe valve.

Once ball seat valve 20 has been opened, fracturing fluid can betransmitted through conduit of tool string 12 to one or more aperturesopened/exposed by valve 20 to carry out fracturing operations on aparticular zone of formation 18 aligned with ball seat valve 20. Thus,seating the ball in the ball seat of ball seat valve 20 fluidicallyisolates a particular zone of wellbore 14 and thereafter valve 20 isopened to allow fracturing fluid to pass through the sleeve into aparticular portion of formation 18.

In some cases, when tool string 12 is run downhole, all of ball seatvalves 20 are initially closed. In one example, thereafter, ball seatvalves 20 are successively opened one at a time in a predeterminedsequence for purposes of fracturing layers of formation 18. For example,ball seat valves 20 are opened in a sequence that begins at the bottomof tool string 12, proceeds uphole to the next immediately adjacentvalve 20, then to the next immediately adjacent valve 20, etcetera.

For purposes of opening a particular valve 20, a free-falling or forcedplug is deployed from the surface of the well into the centralpassageway of tool string 12. In the following examples, the droppedplug is described and illustrated as a spherical ball. However, otherplug types, e.g., differently-shaped plugs may be used.

In one example, the balls deployed for different ball seat valves 20within tool string 12 can have the same diameter. In another example,some or all of the balls can have different diameters. As noted,initially, all of ball seat valves 20 can be closed, and none ofsplit-ring baffles of valves 20 are in a contracted, ball catchingstate. When in the ball catching state, the split-ring baffle of valve20 forms a seat that presents a restricted cross-sectional flowpassageway to catch a ball that is dropped into the central passagewayof tool string 12. Unopened ball seat valves 20 that are located abovethe opened or unopened valve 14 with the split-ring baffle in thecontracted, ball-catching state allow the ball to pass through theconduit of tool string 12.

FIG. 2 is a section view of a portion of tool string 100 includingexample ball seat valve 102. In the example of FIG. 2, ball seat valve102 includes sleeve 106 and split-ring baffle 108. Sleeve 106 of ballseat valve 102 is received within housing 110, which forms a portion ofthe central conduit of the tool string 100.

Tool string 100 includes a number of sections defined by differentcylindrical housings connected to one another. The example of FIG. 2shows only a portion of tool string 100 and it is noted that tool string100 can include a number of additional portions, one or more of whichcan include additional ball seat valves in accordance with thisdisclosure, similar to example tool string 12 and ball seat valves 20illustrated in FIG. 1.

In FIG. 2, tool string 100 includes housing 110, within which sleeve 106of ball seat valve 102 is arranged. Housing 110 is coupled above toupper housing 112 and below to lower housing 114. Housings of toolstring 100, including housings 110, 112, and 114, can be coupled to oneanother in a variety of ways, including, e.g., threaded or splineconnections, interference fits, and other mechanisms for connecting suchcomponents. Housings 110, 112, and 114 form a hollow generallycylindrical casing of tool string 100 that defines central conduit 116,by which fluids can be communicated from the surface, down a wellborewithin which tool string 100 is deployed.

Housings 110, 112, and 114, as well as other components of tool string100 like sleeve 106 can be sealed to one another employing various typesof sealing mechanisms configured to inhibit ingress and egress of fluidsand other materials into and out of central conduit 116 of tool string100. For example, junctions between housing 110 and 112 and housing 110and 114 include one or more O-ring seals 118.

As noted, ball seat valve 102 includes sleeve 106 and split-ring baffle108. Sleeve 106 is received within housing 110 such that the outersurface of sleeve 106 abuts the inner surface of housing 110. Sleeve 106is configured to move longitudinally within housing 110. The centralpassageway of sleeve 106 forms part of central conduit 116 of toolstring 100.

Ball seat valve 102 can be actuated within tool string 100 using avariety of mechanisms. In the example of FIG. 2, tool string 100includes piston 120, which can be configured to actuate ball seat valve102. Piston 120 is arranged and configured to move within upper housing112. In the example of tool string 100, upper housing 112 includes anumber of apertures 122, which expose central conduit 116 of string 100to the surrounding formation.

As described further below, when piston 120 moves in a downwarddirection within upper housing 112, apertures 122 in upper housing 112are exposed to place ball seat valve 102 in an open state, a state inwhich fluid communication occurs between the central conduit 116 and theregion that surrounds tool string 100. Additionally, movement of piston120 downward within upper housing 112 can cause piston 120 to engagesplit-ring baffle 108 and move baffle 108 from the first position withinsleeve 106 to the second position, in which baffle 108 assumes acontracted, ball-catching state. In the example of FIG. 2, multipleO-rings 124 circumscribe the outer surface of piston 120 and formcorresponding annular seals between the outer surface of piston 120 andthe inner surface of upper housing 112, e.g., for purposes of sealingoff radial apertures 122 in upper housing 112 when ball seat valve 102is in the closed state.

FIGS. 3A-3C depict section views and FIGS. 4A and 4B depict perspectiveviews illustrating the structure of example split-ring baffle 108 ofball seat valve 102 and example sleeve 106 of valve 102 in greaterdetail. With reference to FIGS. 2-4C, multiple O-rings 126 circumscribethe outer surface of sleeve 106 and form corresponding annular sealsbetween the outer surface of sleeve 106 and the inner surface of upperhousing 112. Sleeve 106 includes first section 130 and second section132. The inner diameter of first section 130 of sleeve 106 is greaterthan second section 132. The transition between the larger innerdiameter of first section 130 of sleeve 106 and the smaller innerdiameter of second section 132 is characterized by a generally taperedinner surface of second section 130.

Ball seat valve 102 also includes split-ring baffle 108, which is atleast partially received within sleeve 106. Split-ring baffle 108includes longitudinal seam 140 forming two separate circumferential ends142, 144 of baffle 108. As will be described in greater detail withreference to FIGS. 5 and 6 and as shown in FIGS. 3A and 3B, split-ringbaffle 108 is longitudinally moveable between a first position in firstsection 130 and a second position in second section 132 of sleeve 106.The outer surface of split-ring baffle 108 is configured to engage theinner surface of sleeve 106 to allow baffle 108 to be expanded in thefirst position (FIG. 3A), and cause it to be contracted in the secondposition in the sleeve (FIG. 3B).

The outer surface of split-ring baffle 108 is tapered to engage thetapered portion of the inner surface of first section 130. As split-ringbaffle 108 is urged downward within tool string 100, the tapered outersurface of baffle 108 engages the tapered portion of the inner surfaceof first section 130, which causes split-ring baffle 108 to radiallycontract. Radially contracting split-ring baffle 108 in this manner bymoving baffle 108 from the first position to the second position, placessplit-ring baffle 108 in the closed, or “ball-catching,” state. Thus, inthe radially contracted state, split-ring baffle 108 is configured toreceive a dropped ball or other plug to restrict fluid flow throughcentral conduit 116 of tool string 100. Once the ball is lodged insplit-ring baffle 108, fluid pressure can be applied from the surface ofthe well for purposes of exerting a downward force on the ball.

FIGS. 4A and 4B depict split-ring baffle 108 in the radially expandedand contracted states, respectively. As illustrated in FIGS. 4A and 4B,as split-ring baffle 108 contracts from the expanded state,circumferential ends 142, 144 formed by longitudinal seam 140 areprogressively moved closer to one another. In the contracted stateillustrated in FIG. 4B, circumferential ends 142, 144 of baffle 108 abutone another at seam 140. In some examples, however, circumferential ends142, 144 may be offset from one another by a small distance even whenbaffle 108 is in the contracted state.

The tapered portion of the outer surface of split-ring baffle 108 isdefined by tapered surface 150 and tapered tabs 152. Tapered tabs 152protrude outward from and are distributed around the circumference ofone end of split-ring baffle 108. Example split-ring baffle 108 includesfour tabs 152 distributed evenly around the circumference of split-ringbaffle 108. In other examples, a split-ring baffle in accordance withthis disclosure can include more or fewer tabs that are evenly orunevenly distributed around the circumference of the baffle.

Tapered tabs 152 of split-ring baffle 108 can serve a number offunctions. Tabs 152 provide a mechanical stop that can inhibit orprevent baffle 108 from moving axially upward and out of sleeve 106. Asillustrated in FIGS. 3A and 3B, tapered tabs 152 are configured to bereceived by and engage tapered groove 154 in the tapered portion ofsecond section 132 of sleeve 106. As split-ring baffle 108 moves fromthe second position within sleeve 106 to the first position withinsleeve 106, tabs 152 of baffle 108 are configured to engage groove 154in sleeve 106, as baffle 108 expands. When split-ring baffle 108 is inthe second position and expanded, tapered grooves 152 are received inand mate with tapered groove 154.

Tapered tabs 152 can provide another function for split-ring baffle 108in addition to stopping baffle 108 from axial translation beyond sleeve106. As will be described in more detail below, when split ring baffle108 is radially contracted and seated with a ball or other plug and ballseat valve 102 is opened during fracking operations, the pressure withincentral conduit 116 of tool string 100 can reach high levels, e.g.,between approximately 3000 to approximately 5000 pounds per square inch(psi). In such situations, when split-ring baffle 108 is in the secondposition within sleeve 106 and radially contracted, the pressure withinconduit 116 of string 100 can cause the lower end of baffle 108 todeflect radially outward. In the event the deflection of the baffle 108persists and increases past a threshold, the ball seated withinsplit-ring baffle 108 can become dislodged and flow through baffle 108and sleeve 106, thereby opening the fluid restriction achieved by thebaffle and preventing further fracking operations.

Tapered tabs 152 protrude radially outward and structurally support thelower end of split-ring baffle 108 when baffle 108 is in the contracted,ball-catching state. Tabs 152 provide a structure interposed between thelower end of split-ring baffle 108 and the inner surface of sleeve 106,which can act to inhibit or prevent the lower end of baffle 108 fromdeflecting radially outward. Split-ring baffle 108 can be configured towithstand the pressure within central conduit 116 of tool string 100,which can reach high levels, including, e.g., between approximately 1000to approximately 5000 psi. In some examples, an estimated maximumpressure within central conduit 116 of tool string 100 is betweenapproximately 3000 and 5000 psi. However, more commonly, split-ringbaffle 108 can be configured to withstand pressures betweenapproximately 1000 and 2500 psi.

In ball seat valves employed in subterranean fracking operations andother such applications, there is a need for collapsible andre-expandable baffles for use in, e.g., sliding sleeve fracking tools,such as split-ring baffle 108 and other split-ring baffles in accordancewith this disclosure. Wells made with, for example, 4.5 inch casing,balls dropped at the surface preferably have a diameter less than 3.5inches, so the ball can travel through the conduit of the tool string.In such applications, tool string inner diameters, e.g., the diameter ofcentral conduit 116 of tool string 100, may have a need for a diameterequal to or greater than 3.75 inches. Due to these two factors, a baffleemployed as the ball seat in a ball seat valve ideally is capable ofcollapsing from a large diameter of approximately 3.75 inches to asmaller diameter equal to or less than approximately 3.443 inches. Therelatively large amount of baffle diameter travel, which is equal to0.45 inches (3.75−3.3) in the foregoing example, can significantlycomplicate the baffle design.

A number of environmental and operational complications are also presentin such applications, which can also impact the effectiveness of bafflesemployed as ball seats in ball seat valves. For example, theenvironments in which such baffles are employed are often laden withsand. During baffle contraction, segments of the baffle that enable suchcontraction can accumulate sand, potentially preventing full collapse.Additionally, in cemented wellbore environments, segmented designs willtend to collect cement between the segments of the baffle. Moreover,because multiple fracking stages may be pumped through the bafflesbefore they are contracted, erosion of the baffle components can be asignificant concern. Collapsible and re-expandable baffles employed inball seat valves need to be of sufficient strength and flexibility tosupport the pressure load during fracking and to allow for contractionand expansion through the relatively large range of diameters. Also,sealing segments of the baffle that enable contraction/re-expansion canbe important, because segments in the baffle design are potential pointsfor leakage and any leak points can have a jetting effect, which canquickly erode the ball and baffle.

With the foregoing challenges and operational requirements in mind,split-ring baffle 108 is designed to achieve relatively large changes indiameter between the expanded and contracted states, and is alsodesigned to withstand significant loading during fracking operations.Additionally, split-ring baffle 108 includes a single seam 140, thusreducing or minimizing the number of segments the baffle includes. Toachieve large diametrical changes and support high load conditions, insome examples, split-ring baffle 108 is fabricated from a material thatallows baffle 108 to compress from a large diameter to a small diameterand support the loads from the ball impact and the load generated frompressure once the ball is on seat and sealing conduit 116 below ballseat valve 102. In general, split-ring baffle 108 can be fabricated frommaterials with high toughness, or, put another way, materials with highyield strength and low Young's Modulus. The low Young's Modulus enablesa larger change in diameter and higher yield strength enables the baffleto support greater loads. Additionally, high yield strength can alsoassist in allowing larger changes in diameter for split-ring baffle 108.

In one example, split-ring baffle 108 is fabricated from high yieldstrength and low Young's Modulus steel. Example steels from whichsplit-ring baffle 108 can be fabricated include Society of AutomotiveEngineers (SAE) steel grades 4140 or 4130, an austenitic nickel-chromiumalloy (e.g. an Inconel® alloy from Special Metals Corp. of New Hartford,N.Y.), titanium, and a martensitic stainless steel. In other examples,split-ring baffle 108 can be fabricated from other metals. In oneexample, to achieve the desired contractibility and load support,split-ring baffle 108 is fabricated from a material with yield strengthin a range from approximately 100 ksi to approximately 150 ksi and withYoung's Modulus in a range from approximately 16,000 ksi toapproximately 30,000 ksi. A split-ring baffle in accordance with thisdisclosure, including example baffle 108 can thus achieve diametricalchanges on the order of approximately 0.25 to approximately 0.50 inchesand can withstand stresses due to compression on the order ofapproximately 120,000 psi or 120 kilo pounds per square inch (ksi). Inone example, a split-ring baffle in accordance with this disclosure canwithstand stresses due to compression in a range from approximately 70%to approximately 110% of the yield strength of the material from whichthe baffle is fabricated.

It is desirable to have the section thickness of split-ring baffle 108as great as possible. Split-ring baffle 108 can, in certainapplications, be exposed to the effects of erosion where various fluidsare pumped at high rates through central conduit 116 of tool string 100,causing erosion (material losses). Thus, in order to counter or accountfor such erosion effects, it is beneficial to maximize the sectionthickness of split-ring baffle 108 to ensure baffle 108 will allow forthe maximum erosion possible in a given application. Additionally, athicker cross section can also enable split-ring baffle 108 to supportgreater loads, such as loads from the ball, pressure, sealing, etc.

Limiting factors for the cross-sectional thickness of split-ring baffle108 may be the stress introduced into the part when it is fullycompressed coupled with the properties of the material from which baffle108 is fabricated. A thinner cross-section baffle will be stressed lessthan a thicker cross-section baffle, assuming both are compressed to andfrom the same mid-point diameter. Additionally, it is desirable tomaintain a stress on the baffle that is less than the yield strength ofthe material so the baffle is not plastically deformed. Plasticdeformation of the baffle may cause the baffle to have a reduceddiameter when it is re-expanded. Further, if it is necessary to exceedthe yield strength, the second target could be to limit the stress onthe baffle below the ultimate tensile strength of the material fromwhich the baffle is fabricated. If the ultimate tensile strength isexceeded, the baffle can crack or break. Cracks and breakage can alsooccur even at the yield strength of the material. Thus, in order toreduce the possibility of cracks, breakage, and plastic deformation, itmay be best to minimize the stress as much as possible. Thus, in someexamples, it may be desirable to design the baffle cross-sectionthickness such that the stress on the baffle during operation is lessthan the yield strength of the material from which the baffle is made.In some examples, split-ring baffle 108 is designed such that the stresson baffle 108 during operation is equal to or less than approximately80% of the yield strength of the material from which baffle 108 isfabricated.

In some examples, the configuration of split-ring baffle 108 can beanalytically determined or informed using a mathematical relationshipbetween properties of baffle 108 and the stresses that baffle 108 willencounter during use. For example, assuming a split-ring baffle inaccordance with this disclosure is fabricated from a material with aYoung's Modulus, E, of 29,000 ksi and a cross-section thickness, t, anexpanded outer diameter, ODE, and a contracted outer diameter, ODC, thenthe compression stress, σ, on the baffle when in a compressed state canbe calculated according to the following formula.σ=[E×t×(ODE−ODC)]/[(ODE−t)×(ODC−t)]

In the foregoing formula, the section thickness, t, is equal to the wallthickness of the baffle (e.g., [outer diameter−inner diameter]/2). Theformula can be employed to calculate stress at one section of thebaffle. Therefore, in cases where the baffle includes a varying crosssection, the stress can be estimated by calculating stress at a numberof axial sections along the baffle.

The foregoing calculated compression stress, a, on the baffle can becompared to the yield and ultimate strengths of the baffle to determinethe risk of the baffle cracking and/or fracturing. For example, theforegoing calculated compression stress, a, on the baffle can becompared to the yield strength of the baffle to determine if thecompression stress is equal to or less than approximately 80% of theyield strength.

One feature of split-ring baffle 108 that affects the cross-sectionthickness is tapered tabs 152. As illustrated in FIG. 4A and as notedabove, split-ring baffle 108 includes intermittent tapered tabs 152protruding from the circumference of baffle 108. Intermittent tabs 152are employed with split-ring baffle 108, instead of, e.g., a continuoustapered or other shaped lip that extends around the entire circumferenceof the baffle. Intermittent tabs can be provided in examples accordingto this disclosure to provide structural support and mechanicalinterlock functions, while preventing or reducing the risk of baffle 108cracking and/or fracturing when moving between the radially expanded andcontracted states. The presence of a continuous lip around the entirecircumference of the baffle may cause stresses in the baffle that exceeddesign specifications, e.g., exceed 80% of yield strength, which, inturn, can cause cracking and/or fracturing when moving the bafflebetween the radially expanded and contracted states.

As noted above, during fracturing operations enabled by actuation ofball seat valve 102, fracturing fluid communicated down central conduit116 of tool string 100 can act to erode split-ring baffle 108 when thereare any potential fluid pathways in baffle 108 other than the centralconduit through the baffle. As such, portions of split-ring baffle 108that are susceptible to leaking can be coated to assist in sealingbaffle 108 when in the radially contracted, ball-catching state. Forexample, inner ball seat surfaces 146 and 148 of split-ring baffle 108can be coated with rubber to assist in sealing the interface betweenbaffle 108 and a dropped ball from leaking. Additionally, the surfacesof circumferential ends 142, 144 of split-ring baffle 108 can be coatedwith rubber to provide an improved sealed interface between ends 142,144 when the ends abut one another at seam 140 in the radiallycontracted state of baffle 108. A rubber coating on portions ofsplit-ring baffle 144 can also protect the baffle from erosion.

In some examples, a combination of coatings can be employed on portionsof split-ring baffle 144. For example, circumferential ends 142 can becoated with a carbide coating or nikel coating, which can then be coatedwith rubber. The rubber coating applied to baffle 144 can include aDurometer in a range from approximately 40 to approximately 100. In oneexample, the rubber coating includes a Viton (FKM), Nitrile (NBR), orHydrogenated Nitrile Butadiene Rubber (HNBR) coating.

Operation of ball seat valve 102 is described with reference to andillustrated in FIGS. 5 and 6, which are both section views of a portionof tool string 100. In FIG. 5, ball seat valve 102 is in a closed statewith split-ring baffle 108 expanded in the second position within sleeve106. In FIG. 6, ball seat valve 102 is open with split-ring baffle 108contracted in the ball-catching state and with dropped ball 160 seatedin baffle 108.

In practice, split-ring baffle 108 is initially deployed in the firstposition, interlocked with sleeve 106 via tapered tabs 152 and groove154. Baffle 108 is configured to move within sleeve 106 from the firstposition to the second position to cause baffle 108 to assume thecontracted, ball-catching state. For example, split-ring baffle 108 ofball seat valve 102 is at least partially received within sleeve 106 inthe first position. Baffle 108 includes longitudinal seam 140 formingtwo separate circumferential ends 142, 144 in the baffle. The outertapered surface of baffle 108 is configured to engage the inner taperedsurface of sleeve 106 to cause split-ring baffle 108, when in the firstposition to be relatively radially expanded, and, when moved to thesecond position in sleeve 106, to radially contract. Split-ring baffle108 ball seat of ball seat valve 102 can be engaged to move into thesecond position in the radially contracted state such that baffle 108catches dropped ball 160.

Piston 120 arranged and moveable within upper housing 112 of tool string100 is configured to actuate split-ring baffle 108 to move the bafflefrom the open, expanded position to the closed, contracted ball-catchingstate. For example, movement of piston 120 downward within upper housing112 can cause piston 120 to engage split-ring baffle 108 and move baffle108 from the first position within sleeve 106 (FIG. 5) to the secondposition (FIG. 6). In the second position, split-ring baffle 108 assumesa contracted, ball-catching state and is configured to catch droppedball 160.

Movement of piston 120 within tool string 100 can be achieved with avariety of mechanical or electromechanical mechanisms. In one example,piston 120 is dropped within upper housing 112 to engage split-ringbaffle 108 using a hydraulic mechanism. In FIG. 5, a small chamber 162is defined between a portion of the outer surface of piston 120 and theinner surface of upper housing 112. Chamber 162 can be filled with ahydraulic fluid such that the presence of the incompressible fluidprevents piston 120 from being pushed downward within upper housing 112.During fracturing operations using tool string 100, the pressure withincentral conduit 116 remains relatively high, e.g., approximately 2000psi or more when fracking fluid is not being actively transmitted underpressure through the conduit. Thus, in the absence of the hydraulicfluid in chamber 162, piston 120 would be pushed by the pressure incentral conduit 116 from the position in FIG. 5 down to the position inFIG. 6.

In one example, therefore, piston 120 is dropped within upper housing112 to engage split-ring baffle 108 by evacuating the hydraulic fluidfrom chamber 162. When the hydraulic fluid in chamber 162 is removed orsubstantially removed, the pressure within chamber 162 holding piston120 in position is reduced, creating a pressure imbalance between thepressure within central conduit 116 of tool string 100 and chamber 162that causes piston 120 to move down within upper housing 112. Eventuallypiston 120 engages split-ring baffle 108 to move baffle 108 into thecontracted, ball-catching state illustrated in FIG. 6.

The hydraulic fluid can be removed from chamber 162 to actuate piston120 in a variety of ways. In one example, the hydraulic fluid isevacuated from chamber 162 by piercing a membrane that covers an outletport of chamber 162. However, in another example, a small mechanicaldoor or valve can be actuated to open a fluid outlet to remove thehydraulic fluid from chamber 162. For example, an electromagneticmechanism can be employed to pierce the membrane to evacuate thehydraulic fluid from chamber 162 and, thereby, actuate piston 120.

In one example, to actuate piston 120, a magnetic device is deployedwithin a chamber or other passage in tool string 100 that is adjacent toan actuator that is employed to evacuate the hydraulic fluid fromchamber 162. The magnetic device can be a ferromagnetic cylinder orother shaped ferromagnetic material like a ball, dart, plug, fluid, gel,etc. In one example, a ferrofluid, magnetorheological fluid, or anyother fluid having magnetic properties could be pumped to or past amagnetic sensor in order to transmit a magnetic signal to the actuator.Once deployed, the signal(s) generated by the magnetic device can bedetected by a magnetic sensor in tool string 100.

In the event the magnetic sensor detects a signature signal thatcorresponds to deployment of the magnetic device, electronicsincorporated into tool string 100 can be configured to engage theactuator to open the valve, which functions to evacuate the hydraulicfluid from chamber 162 to actuate piston 120 to move within housing 112.For example, if the electronic circuitry determines that the sensor hasdetected a predetermined magnetic signal(s), the electronic circuitrycauses a valve device to open. In one example, the valve device includesa piercing member which pierces the membrane that covers an outlet portof chamber 162. The piercing member that is engaged to pierce themembrane sealing chamber 162 can be driven by any means, such as, by anelectrical, hydraulic, mechanical, explosive, chemical or other type ofactuator. Additional details about and examples of suchelectro-hydraulic valves are described in U.S. Publication No.2013/0048290, entitled “INJECTION OF FLUID INTO SELECTED ONES OFMULTIPLE ZONES WITH WELL TOOLS SELECTIVELY RESPONSIVE TO MAGNETICPATTERNS,” which was filed on Aug. 29, 2011.

In the example of ball seat valve 102, piston 120 also forms a componentof valve 102 in that movement of piston 120 within upper housing 112functions to open valve 102. For example, prior to being actuated,piston 120 covers and seals central conduit 116 of tool string 100 fromapertures 122, which is illustrated in FIG. 5. When piston 120 isactuated by evacuating chamber 162, or by some other mechanism, to movedown, apertures 122 in housing 112 are exposed to place ball seat valve102 in an open state, as illustrated in FIG. 6. In the state illustratedin FIG. 6, ball seat valve 102 is fully actuated with dropped ball 160seated in contracted baffle 108 and piston 120 actuated to exposeapertures 122. In this state, fluid communication can occur betweencentral conduit 116 of tool string 100 and the region that surrounds thetool string, e.g., the formation surrounding the tool within thewellbore. Fracking fluid can then be communicated downhole, throughcentral conduit 116 and can exit apertures 122 to strike the layer ofthe formation surrounding tool string 100.

In the foregoing example, movement of piston 120 down within upperhousing 112 exposes apertures 122 and, thereby, functions to open ballseat valve 120. In another example, however, movement of the sleevewithin which the ball seat is arranged may function to open a ball seatvalve in accordance with this disclosure. For example, movement ofsleeve 106 can cause apertures in housing 110 to be exposed, which canfunction to open the ball seat valve. In such an example, sleeve 106 canbe caused to move within housing 110 either as a result of force exertedby piston 120 or as a result of fluid pressure on sleeve 106 after ball160 has been dropped and lodged in baffle 108.

FIG. 7 depicts a flowchart illustrating an example method of actuatingan apparatus for restricting fluid flow through a downhole tubularmember. The example method of FIG. 7 includes moving a split-ring bafflefrom a first position within a first section of an annular sleeve to asecond position within a second section of the sleeve to cause thebaffle to radially contract (400) and dropping a plug into the bafflewhen the baffle is in the second position and relatively radiallycontracted (402). The sleeve includes an inner surface defining thefirst section of a first diameter and the second section of a second,smaller, diameter. The baffle includes a longitudinal seam forming twoseparate circumferential ends in the baffle. An outer surface of thebaffle is configured to engage the inner surface of the sleeve to causethe baffle, when in the first position to be relatively radiallyexpanded, and, when moved to the second position in the sleeve, toradially contract. The plug is configured to lodge in the baffle torestrict fluid flow through the baffle when the baffle is contracted.

The method of FIG. 7 may form part of a process by which a ball seatvalve in a tool string is closed to restrict fluid flow within a portionof the tool string and to communicate a fracturing fluid out of the toolstring to engage a zone of formation surrounding the string. An exampleof the method of FIG. 7 is described above with reference to FIGS. 5 and6, which illustrate actuation of ball seat valve 102 includingsplit-ring baffle 108, annular sleeve 106, and ball 160 arranged withinhousing 110 of tool string 100.

Various examples have been described. These and other examples arewithin the scope of the following claims.

I claim:
 1. An apparatus for restricting fluid flow through a downholetubular member, the apparatus comprising: an annular housing configuredfor use in a wellbore; an annular sleeve configured to be receivedwithin the housing, the annular sleeve having an inner surface defininga first section of a first diameter and a second section of a second,smaller, diameter; and a resilient split-ring baffle at least partiallyreceived within the sleeve, the baffle comprising a longitudinal seamforming two separate circumferential ends in the baffle, the bafflebeing longitudinally moveable between a first position in the firstsection and a second position in the second section of the sleeve,wherein an outer surface of the baffle is configured to engage the innersurface of the sleeve to cause the baffle, when in the first position tobe relatively radially expanded, and, when moved to the second positionin the sleeve, to radially contract, wherein the sleeve is configured tomove longitudinally from a first position toward a second positionwithin the housing in response to an applied force, and wherein thehousing comprises a plurality of apertures, which are covered when thesleeve is in the first position and uncovered when the sleeve is in thesecond position within the housing.
 2. The apparatus of claim 1, whereinthe two circumferential ends of the baffle are offset from one anotherwhen the baffle is expanded and abut one another when the baffle iscontracted.
 3. The apparatus of claim 1, wherein the two circumferentialends of the baffle are offset from one another by a first distance whenthe baffle is expanded and are offset from one another by a seconddistance that is less than the first distance when the baffle iscontracted.
 4. The apparatus of claim 1, wherein: a first longitudinalend of the sleeve comprises the inner surface, the inner surfacecomprising a tapered profile that defines a transition between the firstsection of the first diameter and the second section of the second,smaller, diameter; at least a portion of a first longitudinal end of thebaffle is received within the first longitudinal end of the sleeve; andthe first longitudinal end of the baffle comprises an outer surfacecomprising a tapered profile configured to engage the tapered profile ofthe first longitudinal end of the sleeve to cause the baffle, when movedto the first position in the first section of the sleeve, to radiallyexpand, and, when moved to the second position in the second section ofthe sleeve, to radially contract.
 5. The apparatus of claim 4, furthercomprising a piston configured to be received within the housing,wherein the piston is configured to move longitudinally within thehousing to engage the baffle to move the baffle from the first positionin the first section of the sleeve to the second position in the secondsection of the sleeve.
 6. The apparatus of claim 5, wherein: themovement of the piston within the housing to engage the baffle to movethe baffle from the first position in the first section of the sleeve tothe second position in the second section of the sleeve causes theapertures in the housing to be uncovered.
 7. The apparatus of claim 4,wherein: the outer surface of the first longitudinal end of the bafflecomprises a tapered surface and at least one tab protruding radiallyoutward from the outer surface; the inner surface of the firstlongitudinal end of the sleeve comprises a groove around thecircumference of the inner surface; and the at least one tab configuredto be received in and engage the groove.
 8. The apparatus of claim 6,wherein the at least one tab comprises a plurality of tabs protrudingradially outward from and distributed around the circumference of theouter surface of the first longitudinal end of the baffle.
 9. Theapparatus of claim 6, wherein the at least one tab comprises an outertapered surface defining at least a portion of the tapered profile ofthe outer surface of the first longitudinal end of the baffle, andwherein the groove comprises an inner tapered surface defining at leasta portion of the tapered profile of the inner surface of the firstlongitudinal end of the sleeve.
 10. An apparatus for communicating afracturing fluid to one or more layers of a formation surrounding asubterranean wellbore, the apparatus comprising: a tool stringcomprising a plurality of annular housings defining a central conduit ofthe tool string through which the fracturing fluid is communicated; anannular sleeve configured to be received within one housing of the toolstring, the annular sleeve having an inner surface defining a firstsection of a first diameter and a second section of a second, smallerdiameter; and a resilient split-ring baffle at least partially receivedwithin the sleeve, the baffle comprising a longitudinal seam forming twoseparate circumferential ends in the baffle, the baffle beinglongitudinally moveable between a first position in the first sectionand a second position in the second section of the sleeve, wherein anouter surface of the baffle is configured to engage the inner surface ofthe sleeve to cause the baffle, when in the first position to berelatively radially expanded, and, when moved to the second position inthe sleeve, to radially contract, wherein the sleeve is configured tomove longitudinally from a first position toward a second positionwithin the one housing in response to an applied force, and wherein theone housing comprises a plurality of apertures, which are covered whenthe sleeve is in the first position and uncovered when the sleeve is inthe second position within the one housing.
 11. The apparatus of claim10, wherein the two circumferential ends of the baffle are offset fromone another when the baffle is expanded and abut one another when thebaffle is contracted.
 12. The apparatus of claim 10, wherein the twocircumferential ends of the baffle are offset from one another by afirst distance when the baffle is expanded and are offset from oneanother by a second distance that is less than the first distance whenthe baffle is contracted.
 13. The apparatus of claim 10, wherein: afirst longitudinal end of the sleeve comprises the inner surface, theinner surface comprising a tapered profile that defines a transitionbetween the first section of the first diameter and the second sectionof the second, smaller, diameter; at least a portion of a firstlongitudinal end of the baffle is received within the first longitudinalend of the sleeve; and the first longitudinal end of the bafflecomprises an outer surface comprising a tapered profile configured toengage the tapered profile of the first longitudinal end of the sleeveto cause the baffle, when moved to the first position in the firstsection of the sleeve, to radially expand, and, when moved to the secondposition in the second section of the sleeve, to radially contract. 14.The apparatus of claim 13, further comprising a piston at leastpartially received within the one housing of the tool string withinwhich the annular sleeve is received, wherein the piston is configuredto selectively move longitudinally within the one housing to engage thebaffle to move the baffle from the first position in the first sectionof the sleeve to the second position in the second section of thesleeve.
 15. The apparatus of claim 14, wherein: the movement of thepiston within the housing to engage the baffle to move the baffle fromthe first position in the first section of the sleeve to the secondposition in the second section of the sleeve causes the apertures in thehousing to be uncovered.
 16. The apparatus of claim 14, furthercomprising an electro-hydraulic valve that is configured to be actuatedto selectively move the piston longitudinally within the one housing.17. The apparatus of claim 14, wherein: the outer surface of the firstlongitudinal end of the baffle comprises a tapered surface and at leastone tab protruding radially outward from the outer surface; the innersurface of the first longitudinal end of the sleeve comprises a groovearound the circumference of the inner surface; and the at least one tabconfigured to be received in and engage the groove.
 18. The apparatus ofclaim 17, wherein the at least one tab comprises an outer taperedsurface defining at least a portion of the tapered profile of the outersurface of the first longitudinal end of the baffle, and wherein thegroove comprises an inner tapered surface defining at least a portion ofthe tapered profile of the inner surface of the first longitudinal endof the sleeve.
 19. A method of actuating an apparatus for restrictingfluid flow through a downhole tubular member, the method comprising:moving a split-ring baffle from a first position within a first sectionof an annular sleeve to a second position within a second section of thesleeve to cause the baffle to radially contract, wherein the sleevecomprises an inner surface defining the first section of a firstdiameter and the second section of a second, smaller, diameter, whereinthe baffle comprises a longitudinal seam forming two separatecircumferential ends in the baffle, and wherein an outer surface of thebaffle is configured to engage the inner surface of the sleeve to causethe baffle, when in the first position to be relatively radiallyexpanded, and, when moved to the second position in the sleeve, toradially contract; and dropping a plug into the baffle when the baffleis in the second position and relatively radially contracted, whereinthe plug is configured to lodge in the baffle to restrict fluid flowthrough the baffle when the baffle is contracted; and moving the sleevelongitudinally from a first position toward a second position within thedownhole tubular member, wherein the downhole tubular member comprises aapertures which are covered when the sleeve is in the first position anduncovered when the sleeve is in the second position within the downholetubular member.